This invention relates to a semiconductor device and a circuit suitable for use in an intelligent power switch.
As used herein the term `intelligent power switch` is to be understood as meaning a semiconductor device in which one or more power semiconductor components are provided in or on the same semiconductor body as logic components for controlling and monitoring operation of the power semiconductor component and a load in circuit with the switch.
An intelligent power switch is described in a paper entitled: `SMART-SIPMOS--an intelligent power switch` by M. Glogolja and Dr. J. Tihanyi published in the Conference Record of the 1986 IEEE Industry Applications Society Annual Meeting Part I at pages 429 to 433.
As described in the aforementioned paper, the intelligent power switch comprises a power MOSFET and high and low voltage CMOS circuitry providing control functions for the power MOSFET. The intelligent power switch described in the paper is intended to be used as a high side switch and so to be connected between a positive power supply terminal, for example the positive terminal of a battery in automotive applications, and the load. In such circumstances, in order to turn the power MOSFET on, a gate voltage for the power MOSFET higher than the battery voltage needs to be generated. In the arrangement described in the paper, the gate voltage is generated using a drive circuit which consists of a charge pump, rectifier and level shifter. Thus, during a first half of the alternating cycle of an oscillator a capacitor C1 of the charge pump shown in FIG. 3 of the aforementioned paper is charged to almost the full battery voltage via IGFET Q4, diode D5 and IGFET Q7. During the second half of the cycle, the left hand side plate of the capacitor C1 is switched by IGFET Q3 to the battery positive terminal potential so that the charge from C1 is transfered via an IGFET Q5 acting as a rectifier to the gate of the power MOSFET and, after a given number of cycles of the oscillator a reasonable gate source voltage is reached to turn on the power MOSFET.